Magnetostrictive four-pole



Aug. 19,'1952 H. BLOCH MAGNETosTRIcTIvE FOUR-Pom:

2 SHEETS-SHEET 1 lFiled Aug. 1e, 1951 vINVENTORI ATTORNEYS.

Aug 19, 1952 H. BLOCH 2,607,814

MAGNETOSTRICTIVE FOUR-POLE Filed Aug. 16,11951 2 SHEETS-SHEET 2 i; Y Y A l ,If I

Patented vAug. 19, 1952 MAGNETOSTRICTIVE FOUR-POLE Heinz Bloch, Wettingen, Switzerland, assigner to Patelhold Patentverwertungs- & Elektro- Holding A.G., a joint stock company, Glarus,

Switzerland Application August 16, 1951, Serial No. 242,111 In Switzerland August 22, 1950 13 Claims. 1

The present invention relates to magnetostrictive devices and in particular to those of the type comprising a bar made from magnetostrictive material mounted at a vibration node and longitudinally oscillating, the bar being supported intermediate its ends by a bearing and a coil surrounding the bar on each side of the bearing. The bar is premagnetized by one or more permanent magnets and the terminal ends of the two coils (four in number) Vform what is commonly known as a .four-pole.

Such four-poles have various uses such for example as wave filters or as frequency stabilizers, and are described in ldetail in various patents'such as Swiss Patent No. 197,694 and United States Patent No. 1,750,124.

The mounting of the bar. as experience has shown, causes dfliculties because two contradictory requirements must be met. On the one hand, the'bar mounting should allow the bar full freedom of movement in the longitudinal direction, also for Vmounting at a node, this being necessary in consideration of the practically never perfect immobility ofthe node in the bar. On the other hand,however, the bar must be secured crosswise to the longitudinalv axis as xedly as possible in order that existing air gaps between the magnetostrictive bar and the one or more premagnetizing permanent magnets and also any air gaps provided in the flux return Yokes will remain unchanged while the bar is oscillating. Moreover, also the coils energizing the' bar shouldbe capable of being Awound vas close to the bar as possible without touching the same, and this again requires an accurate and laterally fixed mounting of the bar. In addition,V

the entire four-pole should form a structural unit which as a whole iseasily exchangeable and is sturdy enough to be capable of being used in portable equipment.

The two extreme requirements concerning the mounting of the bar can be fulfilled according to the present invention by providing a circular disc on the bar at the node where it is to be mounted and clamping the disc itself at its rim portion to al support. The bar is thereby mounted crosswise to the longitudinal axis with suicient resistance to lateral displacements. The disc should beV proportioned with respect to thickness' and diameter ina manner such that one of its inherent frequencies coincides with the inherent frequency of the bar with which the bar is magnetostrictively energized. For example, the bar may be allowed .to Aoperate, in its fundamental frequency (one'node in the center of the bar),

dimensioning the disc in such awayv that also the fundamental frequency of the disc coincides with the fundamental frequency of the bar. However, as a working frequency for the disc there may be selected for example the frequency of its third harmonic and asfa working frequencxT for the bar for example the frequency of its fth harmonic, and it is thenl merely necessary to fulfill the condition that the workingv frequencies of the disc and bar coincide.

All of the conditions mentioned can be fulfilled by the present invention, namely in that a circular disc, whose working frequency in the case of rigid insertion of the disc rim corresponds to the working frequency of the longitudinally oscillating bar, serves as a bearing for the oscillating bar, in that this bearing disc is provided in the center of the bar concentrically thereon, and that there are connected with the rim portion of the bearing disc three non-magnetizable bolts which extend on both sides of the bearing disc parallel with the oscillating bar, in such a way that the centers of the three bolts form the edges of a prism having the cross section of an equilateral triangle, the longitudina1 axis of the prism and of the oscillating bar coinciding, and that at the free ends of the three bolts there is provided on both sides of the bearing disc and parallel with this disc an end plate for each, there being installedbetween each end plate and the bearing disc one of the said coils concentrically withthe oscillating bar and there being inserted on both sides of the bearing disc at least in one of the three spaces between each pair of adjacent bolts acylindrical permanent magnet parallel with the oscillating bar and there being installed in at least one of the remaining free spaces a magnetizable Vbar which servesas regulable shunt yoke for the magnetic iiux'between the bearing disc and the end yokes.

In the drawings which illustrate alternative embodiments of the invention: p y

Fig. 1 isa Vertical central section taken on line l-I of Fig. 2 showing a construction adapted particularly for use with frequencies below 50 kilocycles;

`lFig. 2 is a horizontal section on line 2 24 of Fig. 1; I

Fig. 6 is a vertical View partly in section illustrating another modified construction.

With reference to Figs. 1 and 2 in particular, the magnetostrictive four-pole is seen to be comprised of a straight cylindrical bar I of magnetostrictive material, the composition of which is discussed hereinafter. Intermediate the ends of bar I and around the same is positioned a circular bearing disc 2 of magnetizable material, the bar and disc being concentric, and the central hole in the disc through which the bar passesv being of substantially the sameA diameter as the bar to provide a tight press t therebetween. Three bolts 3 of a non-magnetizable material such as for example brass, are rigidly connected with the rim portion of disc 2 which, is preferably reinforced by annular discs 4, 4' applied to opposite faces thereof and held in position by the bolts 3 each of which as illustrated is divided into two halves secured together with the reinforcing discs 4, 4'- and disc 2 secured therebetween.

As; is evident from Fig. 2,7the centers of the three bolts 3 form the edges of a prism which presentsV in transverse section the form of an equilateral triangle through the center of which passes the axisof'bar IV which extends parallel to the bolts 3. I

The upper and lower ends of the three bolts 3 terminate in threaded sections; I4secured by nuts I4 to end plates '5, and they latter are provided I with axiall apertures through which the bar I passes; Theg apertures inthe plates 5 are preferablyV of substantially the same diameter as that of bar I so as to; provide a pathy of loW reluctance for the magneticv flux produced in the bar I to passl into,` the plates 5. Some radial clearance between bar I and endcplates.y 5; is however neces- Sary.

For energizing barV I magnetically,V two coils 6- are utilized. Each,` coil is carriedV on a spool 7 arrangedconcentrically on the bar and one of the; coils is arranged below andthe other above the centrally located disc 2:.

Extending between central disc 2 and each of the end platesv 5; is, aA permanent magnet in the form lof aY cylindrical bar. The magnet bars 8., Bf have their outer ends secured to plates 5 by screws 9 ,L are arranged coaxially and parallelwith the bar I of magnetostrictive material, and are disposed in any one of the three-spaces between any two. adjacent bolts 3. In the two` remaining spaces between the bolts 3f, are arranged cylindrical bars I 0 of .magnetizable material. Bars I0 which extend parallel to` bars I and 8, 8 are secured rigidly at their inner ends to the reinforcing discs 4, 4 and their outer ends terminate short of the end plates 5 to establish air gaps I2 the lengths of which can be made adjustable by screws II axially aligned With the bars I0 and which thread through the plates 5. The bars I0 and screws II thus constitute a shunt yoke for regulation of the premagnetization of bar I from the permanent magnets 8, t. If desired, to increase the premagnetizing effect of bar I, a second set of permanent magnet bars 8, 8 may be used in place of Vone of the sets of magnetizable bars I0. The component assembly as described is preferably enclosed by a cup-shaped casing I3 to make it dust proof. the casing being divided axially into two halves which t into a centrally located ring I5. The threadedl ends I4 of bolts3 extend through the end walls of thecasing halves and areV anchored there by nuts I4" which when tightened press the halves of the casingtowards each other into the ring I 5. Ring I 5 also serves to support the connecting terminals I6 for the coils 6.

The electrical properties of the magnetostrictive four pole shown in Fig. 1 are as follows.

If to one of the two coils 6 there is connected an alternating voltage of constant maximum amplitude Whose frequency of alternation is variable between fl and f2, a voltage is obtained at the terminals of the other coil 6 having a variation dependent upon the said frequency and which varies according to the curve U shown in Fig. 3. Thefrequency fo corresponds to the frequency to which both the bar I and bearing disc 2 are tuned, theworking frequency corresponding in the present example to the frequency of fundamental vibration both of bar I and disc 2.

From thel curve in Fig. 3, the Q factor of the fourpole can be determined according to the equation for asv a result; of the AE l effect. discussed below, all` curvesbeing plotted" asza function ofthe change. in premagnetization field strength H. Dependentl upon the selection of I-Itherefore, the. four polepresents different. properties. In zoneI. (up. to the broken vertical boundary line of premag.- netization. field'l strength value H); the Q factor and the factor is relatively-high, thevoltage Uisrelatively low, y

Y 5f i f o; is relatively high. The possibility ofA compensa;- tion by the AEV effectlies inJ the orderofimagjnitudeA 103lA Inv4 zone VIll' (to thej right, of' the broken vertical line value ofpremagnetization field strength H) theQ-factoris somewhat, lower but the voltage transmissions Uf" isnincreased and factorv 1 Y v fo A is smaller for a1 given changei'nVVV frequency ofthe field variations;

Since for givenr dimensions. the disc 2P andi 'bar I5 possess av certain-l` working frequency, means must: be provided totune 'thefinishedfour*` poleY accurately to a desiredl'rtheoretical frequency; For thispurpose the propertyof' ferro-magnetic materials; known; as` AE effect/jean be utilized; The modulus of elasticity asafunetionofthepremagnetization is; in fact', not `a constant; andL therefore, by Varying, 'the premagnetization ofbar Isthemoduluspfrelasticity;thereofandhence its inherent c natural: frequency: of?- vibration1 canL be. variedl within narrow; limits.v Thepr'emag-L netization from .magnets 8; 8` can.v be varidf byv 5 an air gap in the circuit of the premagnetization flux. For this purpose there serves the air gap adjustable with the aid of thescrew I I in the shunt yoke Ill as previously explained.

If desired, the premagnetization of the magnetic circuit by the permanent magnets can be made adjustable by providing an adjustable air gap between one end of the magnet 8a. and an adjustable screw I3a threaded into the end plate 5a, as shown in Fig. 6, the opposite end of magnet 8a, being secured to the annular disc 4a.

Depending on the desired intensity of the premagnetization of bar I it is possible to replace the yokes I by permanent magnets. Thus one,

two, or three permanent magnets can be installed in the arrangement on each side of the bearingdisk between the bolts 3 as previously explained.

Since the frequency constants of the four-pole when used as wave lter or as vibration stabilizer must be as great Aas possible also in the case of temperature fluctuations, certain requirements must be observed in selecting the material of the bar I. For the bar I a material should be selected whose temperature coeiiicient of its modulus of elasticity is at least equal to its temperature coefficient of linear expansion but with opposite sign, i. e. one coefficient is negative and the other positive. Under such conditions the change in frequency of the magnetostrictively energized bar per degree change in temperature will be practically zero. Experiments with a bar of Elinvar (an alloy of about 49% Fe, 36% Ni, 12% Cr, .5% Si, 1% C) have shown that after suitable thermal treatment (annealing to about 850 deg. C.) a frequency variation of less than 1X1()-6 cycles per deg-ree is obtainable.

As can be seen from Fig. 1, the bar I must not shift crosswise to its longitudinal axis, as this may easily cause distunbances in the vibration as soon as the bar touches the spools 1 or the end plates anywhere. If one selects for the disc 2 a material whose coefcient of expansion is smaller than that of the material of the bar I (e. g. Invar, an alloy of 36% Ni and 64% Fe) and if one presses the disc onto the bar at a temperature below the mean operating temperature, one obtains at the operating temperature an insertion which is sufficiently rigid and stable to prevent cross dis-placements of the bar I.

The embodiment of the invention shown in Figs. 1 and 2 can be used for frequencies in the range below 50 kilocycles. For frequencies between 50 and 500 kilocycles the embodiment according to Fig, 5 is especially suitable. In accordance with the higher working frequencies and the consequent shorter dimensions of the bar I', also the bearing disc 2 should be proportionally thinner. In order to be able to make the .edge of this disc rigid nevertheless, it is advisable to provide the disc not with the clamping discs 4 shown in Fig. 1, but rather with a thickened rim 42a. In this rim the bolts 3 may be fastened and formed as in Fig. 1. However, a construction as per Fig. 5 may also be used, consisting of an inner bolt 20 with sleeves 2| thereon. In a central bore in the upper and lower end plates 5 a `set screw 22 is provided whose axis points in the direction of the longitudinal axis of the oscillating bar I and is separated from the end face thereof by the air g-ap 23. This arrangement has two advantages. First, the space between each end fplate 5' and disc 2' can be made suiciently long to install the coil body (not shown) even if the bar I is short (that is, if the frequencies are high). Second, the set screws 22 permit a fine regulation o- 6 of the inherent natural frequency of the bar I' even whenit is desired to press the permanent magnets 8" and bars I0' simply :between the end plates 5' and the disc 2', omitting the set screws 9andIIofFig.1. A l

In Fig. 5, however, a casing I3 is shown (partially broken away) which is pressed in a base plate `24 so as to be dust-proof, this base plate supporting at the same time the four connection terminals 25 for the coils, thus being designed` like the multi-pronged base of a conventional vacuum. tube.

Instead of tuning the bar I and the disc 2 with each other on their fundamental frequency, other combinations are of course also possible, for example, the fundamental frequency of the plate 2 can Vbe tuned on the frequency of a harmonic (for instance the third or the fifth), this being advisable when it is desired to work with such high frequencies that a bar working at the fundamental frequency would be too short to be handled conveniently. A more detailed discussion of tuning the plate and :bars can be found in the literature available on this subject such as Huttes Des Ingenieurs Taschenbuch."

In conclusion, it is to be understood that while the foregoing illustrated embodiments of the invention are to be preferred, various changes in the construction and arrangement of component parts may be devised by those skilled in the art without however departing from the spirit and scope of the invention as defined in the a-ppended claims.

I claim:

l. A magnetostrictive four-pole comprising a bar of magnetostrictive material, a circular bearmg disc of magnetizable material mounted concentrically upon and rigidly connected with said bar intermediate the bar ends, the Working frequency of said mounted disc corresponding to the working frequency of the longitudinally oscillatable bar, three bolts of non-magnetizable material extending from the rim portion of said disc in opposite directions parallel with said bar, said bolts being so spaced about the axis of said disc as to form the edges of a prism having the cross section of an equilateral triangle and whose axis coincides with the axis of said bar, end plates of magnetic material parallel with said bearing disc and secured to the opposite ends of said three bolts, cylindrical coils concentric with and surrounding said bar respectively between said bearing disc and said end plates, a permanent bar magnet arranged longitudinally of said magnetostrictive bar between said bearing disc and each of said end plates in one of the three spaces between each pair of said bolts, and at least one bar of magnetizable material arranged longitudinally of said magnetostrictive bar between said bearing disc and each of said end plates in one of the two remaining spaces between each pair of said bolts, said last bars functioning as a shunt for the magnetic flux which flows in said magnetostrictive bar.

2. A magnetostrictive device as defined in claim 1 wherein said bearing disc is provided with annular members secured to opposite faces thereof at the rim portion to reinforce the same.

3. A magnetostrictive device as dened in claim 1 wherein said bearing disc has a thickened rim portion to reinforce the same.

4 A magnetostrictive device as defined in claim 1 wherein said three bolts each consist of two halves joined together in end to end relation '7 at. saidrbearing d isc with` the latter Vclampedv therebetween.v l

. 5..A. :mafgnetostrictive deviceV as defined.. in

claim 1 wherein said three bolts each are continuous between said end plates passing through apertures in saidbearing disc and-which further include. afsleeve surrounding each boltk between. thebearing disc andend` plates, saidlbearing disc beingclamped. between the two sleeves. of each bolt. V

6. A magnetostric'tlve devicev as defined in. claim 1 wherein the ends of said magnetostrictive bar pass at least partially through axial a-pertures Ain said endplates.`

7. A. magneto'strictive device as. defined in claim 1 wherein. the` endsof. said. magnetostrictive bar. terminateY s'hortfofQsaid. endy plates and whereineach said end plate is provided withl an axially disposedserew adjustable longitudinally and confronting`- thefend faces ofv said magnetizable bar toesta-bli'slfrr an adjustable. air gap therebetween. A

8. A 'magnetostrictive deviceA as defined in claim l wherein thesaid-magnetizable bars constitu'ting said ux shunt are'each secured. at one end to said bearing disc, the'other end thereof terminating short of thefassociated. end plate, and screws adjustable longitudinally in-said.. end plates and confronting ther end faces of said` magiiet'i'zableY bars to establish` adjustable air gaps therebetween.

. 9. A magnetostrictive device as defined in claim 1 wherein saidV bar magnets are clamped between the rim portion of said bearing disc and the associated end plate.

10. A` magnetostrictive device as defined. in claim 1 whereinfsaidv bar magnets are each lsecured atV one end. thereof to said bearing dise, the. other endv thereof.'v terminating short of the associated end plate, and screws adjustable longitudinally in said end plates and confronting the endiaces of said bar magnets to establish adjustable air gaps therebetween.

11..A` magnetostrictive device as dened in claim 1.V and which further includes a two-part cup-shaped casing therefor, the two casing halves being connected by aring.' surrounding saidbearing disc.

12. A` magnetostrictive device as dened in l claim: 11A wherein saidring supportsthe electrical terminals. connected tothe four terminal ends of the saidvtwo coils.

13. A magnetostrictive device as deiined in claiml and whichffu'rtherv includes a cup-shaped.

N o references Cited'. 

